Some attempts have been made to make broad or bimodal molecular weight distribution polyethylene in two (2) reactors. In U.S. Pat. No. 5,032,562, a bimetallic catalyst system is described that produces broad or bimodal molecular weight distribution polyethylene resins in a single reactor. In that catalyst, the LMW component is produced by the Zr site while the HMW component is produced by the Ti site. The relative productivity of the two transition metal sites determines the weight fraction of the HMW and LMW components in the final product.
The final product is a gel-free intimate mixture of these two components because of the close proximity of the two metal sites in that catalyst. In that product, the weight fractions of the HMW and LMW components in the final product are fixed by the relative concentration of the two metal species in the bimetallic catalyst. It is often desirable to change the weight fraction of either the HMW or LMW components produced by the bimetallic catalyst in the single reactor. Reformulation of the bimetallic catalyst offers one mode of operation, to change the relative weight fraction of one of the two components produced by such a catalyst.
It is an object of the invention, to eliminate time consuming and costly capital investment in employing two reactors in tandem to produce bimodal molecular weight distribution resins of target molecular weight.
It is another object of the invention, to eliminate time consuming catalyst reformulation procedure(s) to alter the concentration and productivity of the two metal sites of the catalyst.